Various three-dimensional display architectures exist. Spatial 3-D displays such as Actuality Systems Inc.'s Perspecta® Display create 3-D imagery that fills a volume of space and that appears to be 3-D to the naked eye. One such spatial 3-D display is described in U.S. Pat. No. 6,554,430, “Volumetric three-dimensional display system.” This display is formed in the shape of a transparent dome and contains a rotating screen orientated vertically within the dome as shown in FIG. 1. As the screen spins it displays a previously recorded image for example at every 1 degree of rotation for 360 degrees. Human persistence of vision combines these images to create a 3-D view of the previously recorded image. This display with its vertical dome shape can be placed on top of a tabletop for example. One feature of this type of 3-D display is that the imagery provides motion parallax in every direction; in other words, it is a fill parallax display.
Some 3-D displays provide motion parallax information with only one degree of freedom. A well-known family of 3-D displays with restricted motion parallax are horizontal parallax only (HPO) displays. Known HPO displays provide motion parallax along one axis, normally in the horizontal direction, corresponding to left-right motion; when the user moves vertically, the 3-D image appears to track the user's motion because of the lack of vertical parallax information. Displays of this type are taught in: U.S. Pat. No. 3,178,720, “Three dimensional unaided viewing method and apparatus,”; D. J. DeBitetto, “Holographic Panoramic Stereograms Synthesized from White Light Recordings,” in Applied Optics, Vol 8(8), pp. 1740-1741 (August 1969); and U.S. Pat. No. 5,132,839, “Three dimensional display device.”
Another type of restricted parallax display can be called the theta parallax only (TPO) display, which provides motion parallax for a user moving angularly around the display. A 360-degree hologram is a display hologram of this type, as described in R. Hioki and T. Suzuki, “Reconstruction of Wavefronts in All Directions,” in Japanese Journal of Applied Physics, Vol. 4, p. 816 (1965); and in T. H. Jeong, P. Rudolf, and A. Luckett, “360° Holography,” in Journal of the Optical Society of America, Vol. 56(9), pp. 1263-1264 (September 1966). A cylindrical hologram is another display of this type. As taught in the present application, one embodiment described below is a new example of a TPO display and is a circular display located in a top or in the middle of a table for use with multiple users sitting around a conference room table.
Volumetric 3-D displays, such as that described in U.S. Pat. No. 6,554,430, create volume-filling 3-D imagery that can be seen from almost any viewing position. However, as its projection screen is an omnidirectional diffuser, the light from each projected 3-D pixel is scattered in all directions. The consequence of this is that every 3-D scene appears transparent. In contrast, the present invention may include a volumetric 3-D display which projects 3-D pixels that do not necessarily appear transparent because the emission profile for each 3-D pixel is “programmable” along at least one axis of motion parallax.
Additionally, the Perspecta® display as shown in FIG. 1, ordinarily functions as a high-resolution multiplanar volumetric display. Normally, a 3-D dataset is generated by “slicing” the desired 3-D scene into 198 radially disposed slices, with a resolution of 768×768 voxels per slice. A fast spatial light modulator, such as the Texas Instruments (Plano, Tex.) Digital Mirror Device™ system 120, illuminates an isotropic diffusing screen 190 with the sequence of slices while the screen rotates at 600-1000 rpm. The SLMs are stationary, but several relay mirrors 10 rotate with the screen because they are mounted to a “cake pan” 160. The user perceives 3-D imagery because the eye's integration period is slow enough to treat the assembly of voxels as a unified 3-D scene. The Perspecta® display ordinarily uses a 3-DMD projector 120 to illuminate a diffuse screen 190 via several relay mirrors 10.
Although the Perspecta® display creates high-resolution imagery with full parallax, it does not generate imagery with viewer position-dependent effects such as hidden-surface removal for several simultaneous users. The reason for this is that the diffuser screen treats each voxel as an omnidirectional emitter. To explain, in FIG. 1A illustrates the top view of a scene composed of a single cube. An observer looks at 3-D pixel A on Face A. If the cube is desired to appear opaque, then the observer at that location should not see 3-D pixel B on Face B. In contrast, FIG. 1 and FIG. 1B show why volumetric displays with omnidirectional diffuser screens are incapable of rendering opaque features. A screen 190 rotates about axis of rotation 170. At time t1, 3-D pixel B is projected and radiates visibly in all directions. Some of that light will enter the eye of the observer. At a later time t2, the screen has moved and light from 3-D pixel A is projected which also enters the eye of the observer. Therefore, the observer effectively sees a superimposition of 3-D pixels A and B. Clearly a new approach is needed to “program” or control the radiative characteristics of each 3-D pixel in a reconstructed 3-D scene. Additionally, the imagery suffers from a vertical “dead zone” due to limitations of the scattering profile of the diffuser screen. This application offers several solutions to these problems.